Temperature sensors are often used in the field of automation technology, e.g., in order to sense the temperature of a medium in a pipeline and/or in a container, or in field devices, such as thermal flow-measuring devices for measuring the flow rate and/or the density of a medium in a pipeline. Temperature sensors comprise a temperature-sensitive component, e.g., a resistance thermometer or a thermal element, as well as cables, wherein these components are often inserted into a measuring tube. Corresponding temperature sensors and field devices are produced and marketed by the applicant. The underlying measurement principles of the temperature sensors and of the field devices are known from a multitude of publications.
Multipoint sensors for measuring temperature consist of a plurality of individual temperature sensors and allow for the simultaneous measurement of locally spaced-apart measurement points of a temperature profile of the medium.
In the industrial environment, high demands in terms of robustness, reliability, and measurement accuracy are imposed on the temperature sensors. For this purpose, the temperature sensors are often integrated into mineral-insulated lines—in particular, in applications with high temperatures, aggressive media, and/or high process pressures. Sheathed cables in which an element to be insulated—in this case, one or more temperature sensors—is completely surrounded by a ceramic insulating material are called mineral-insulated lines.
Mineral-insulated lines are generally produced by mechanical pultrusion processes, by means of which the desired shape of the line is formed after a series of deformation steps. Prior to the pultrusion process, the temperature sensors are inserted into ceramic blocks, which are crushed into a powder during the pultrusion process. This powder forms the insulating material and allows a bending of the mineral-insulated line up to a certain degree.
A disadvantage in this production method is that only mechanically robust, temperature-sensitive components, such as thermal elements, can be used. Less robust types of temperature-sensitive components, such as resistance thermometers, would be damaged as a result of the great forces that prevail during the pultrusion process.
A basic disadvantage of mineral-insulated lines also consists in the insulating material slowing down the heat flow from a process medium to the respective temperature sensor located in the line. A temperature change in the process medium is thus sensed with a time lag by the respective temperature sensor.
In the case of a multipoint sensor, in which several temperature sensors are located in the mineral-insulated line, a locally-precise sensing of the individual measurement points of a temperature profile is, moreover, difficult, due to the insulating material surrounding the temperature sensors.